1. Field of the Inventions
The inventions relate to molds for producing articles. More specifically, these inventions relate to methods and systems for controlling mold temperatures.
2. Description of the Related Art
The use of plastic containers as a replacement for glass or metal containers in the packaging of beverages has become increasingly popular. The advantages of plastic packaging include lighter weight, decreased breakage as compared to glass, and potentially lower costs. The most common plastic used in making beverage containers today is PET. Virgin PET has been approved by the FDA for use in contact with foodstuffs. Containers made of PET are transparent, thin-walled, lightweight, and have the ability to maintain their shape by withstanding the force exerted on the walls of the container by pressurized contents, such as carbonated beverages. PET resins are also fairly inexpensive and easy to process.
Most PET bottles are made by a process that includes the blow-molding of plastic preforms, which have been made by processes including injection and compression molding. For example, in order to increase the through-put of an injection molding machine, and thereby decrease the cost of each individual preform, it is desirable to reduce the cycle time for each injection and cooling cycle. However, the injected preform must cool sufficiently to maintain its molded dimensions before it is removed from the injection mold. Therefore, it would be desirable to utilize a cooling system that can rapidly cool the injected preform. Typically, the temperature of the mold is controlled by pumping cooled water through passages which are within the mold. The temperature of the mold is thus controlled by the temperature of the water flowing through the water passages. The water typically flows continuously throughout the molding operation and may cause condensation to form on the mold. For example, when the mold is cooled by utilizing chilled water, the moisture in the air surrounding the mold can condense, thereby forming condensation on the molding surfaces. The condensation may interfere with the molding operation by reducing preform production and decreasing preform quality. As a result, the potential of mold cooling systems has not been realized.